A process for chlorinating titanium-containing materials in a fluidized bed reactor is known. Suitable processes are disclosed in patents U.S. Pat. No. 2,446,181; U.S. Pat. No. 2,701,179; U.S. Pat. No. 3,591,333; and U.S. Pat. No. 3,883,636. In such processes, chlorine, particulate coke, particulate titanium-bearing materials, chlorine and optionally oxygen or air, wherein at least one of these contains sulfur, are fed into a fluidized bed reactor under conditions which chlorinate the titanium and many of the other metallic impurities. Gaseous titanium tetrachloride, other metallic chlorides, carbon monoxide (CO), carbonyl sulfide (COS), carbon dioxide (CO2) and other gaseous products exit the fluidized bed reactor. The gaseous titanium tetrachloride produced can then be separated from the other metal chlorides and impurities and oxidized to titanium dioxide, a white pigment, or further processed to produce titanium metal.
Details of fluidized bed processes for chlorinating titanium containing materials are disclosed in U.S. Pat. No. 5,585,078 ('078). The '078 patent also discloses and claims a process for reducing the emissions of CO and COS from the fluidized bed reactor effluent. The emission reduction process involves introducing an oxygen containing gas into at least one location which is downstream of the surface of the fluidized bed, as measured in its static condition, with the oxygen containing gas being introduced in an amount to convert at least some of the COS and CO to CO2 and SO2 which reduces CO and COS emissions. In the example given in the '078 patent, the CO emitted from the fluidized bed chlorinator was reduced by 36.7%, and the COS was reduced by 92.5%.
In the titanium chlorination process, it is desirable to convert COS to SOx, where x is 2 or 3, and CO to CO2, because environmental requirements often require low levels of emissions for CO and COS. However, as stated in U.S. Pat. No. 4,961,911, while means are known to reduce the amount of carbon monoxide emitted, they involve addition of compounds which can be undesirable in the titanium dioxide pigment or in the process to make such pigment.
Carbonyl sulfide (COS) is known to be a fairly inert chemical compound. Furthermore, carbonyl sulfide is a known poison for many supported metal oxidation catalysts. Because of the above, catalytic oxidation of CO in the presence COS is a difficult problem.
There is a need for an efficient catalytic process for the oxidation of carbon monoxide to carbon dioxide in the presence of carbonyl sulfide and also to simultaneously oxidize carbonyl sulfide to sulfur oxides.